Native tree shuts out volcanic pollution

The past week marked the celebration of the 42nd annual Merrie Monarch Festival on the island of Hawai`i. Throughout the seven-day cultural event, participants and spectators can be observed wearing beautiful lei, many created with native Hawaiian plants. Particularly notable are lei incorporating the striking yellow, orange or red lehua blossoms of the `ohi`a lehua tree, and its reddish colored young leaves, or liko lehua. Another often-used plant, the a`ali`i, produces colorful seed capsules that enhance the fullness of a braided or wrapped lei (lei haku or lei wili).

An interesting scientific discovery was made regarding these two species of plants during the early years of the festival. In 1979, during Kilauea’s brief (40-hour) upper east rift zone eruption at Pauahi Crater, researchers examined the effects of volcanic fume on the adjacent forest stand. They found that the `ohi`a lehua (Metrosideros polymorpha) and the a`ali`i (Dodonaea viscosa) varied greatly in their susceptibility to sulfur dioxide. This is the primary noxious gas in the Kilauea plume and the main contributor to volcanic pollution, known locally as vog. While sulfur dioxide gas is known to injure foliage, the researchers found that the `ohi`a lehua has developed a clever adaptation to minimize injury.

In contrast to the delicious Hawaiian plate lunches that are available to festival-goers, plants use water, carbon dioxide, and light energy to make carbohydrates through photosynthesis for their nourishment. Carbon dioxide enters the plant’s leaves through pores in the leaves’ waxy outer surface. These pores are aptly named stomata, after the Greek word for “mouth.” When the stomata are open, gases diffuse into and out of the leaf, while closed stomata inhibit gas exchange.

In examining plant communities downwind of the eruptive vent, researchers found that visible injury diminished with increasing distances. SO2 concentration also decreased downwind as the plume dispersed and was diluted. The pattern of injury for a`ali`i was typical of about 20 other species abundant in the area. Most of the plants were severely injured or dead 50 yards from the eruptive vent, while approximately 1 mile downwind, there was no sign of dead or even yellowing leaves.

In contrast, mature leaves of the `ohi`a lehua exhibited no symptoms of damage, even close to the vent. The leaves showed more stomatal closure when exposed to higher concentrations of noxious sulfur dioxide gas. Young `ohi`a leaves, however, were severely injured close to the eruptive vent, with the few survivors showing only partial stomatal closure.

The stomata in the a`ali`i leaves did not close at all in response to sulfur dioxide, and the plants were severely injured by exposure to high concentrations of the pollutant. However, new leaves of this tenacious plant resprouted quickly after the damage, enabling recovery.

SO2 concentrations between 0.1 and 1 ppm are known to cause rapid changes in the stomatal opening for a wide range of plant species. This is an important adaptation, since many plants are exposed to man-made sulfur dioxide pollution. The exposures for the `ohi`a and `a`ali`i studied in the natural volcanic environment of Hawai`i, ranged from less than 1 ppm to greater than 100 ppm SO2.

Recently, increases in the gas emission rate from Kilauea, in combination with a lack of trade winds, has caused high concentrations of SO2 in areas of East Hawai`i. Last Saturday, during a particularly notable event, SO2 concentrations reached nearly 3 ppm at Hawai`i Volcanoes National Park Visitor Center.

While some residents reported discomfort, and certain exotic plants showed signs of stress and burned leaves, this brief event caused little impact to native forest plants. Evolving in a volcanic environment has engendered creativity in endemic plant adaptations, at the same time it allows us all to enjoy the beauty of these plants, especially during Merrie Monarch week.

Activity Update

Eruptive activity at Pu`u `O`o continues. The Pu`u `O`o crater camera is offline for repair.

The PKK flow continues to produce substantial breakouts from atop Pulama pali to the coastal plain. Open lava channels have been visible intermittently on Pulama pali and on the west and east branches of the PKK flow. Lava is currently entering the ocean at four areas. Highcastle, East Lae`apuki, Kamoamoa, and Ka`ili`ili entries are about 3.7 km (2.3 miles), 4.9 km (3 miles), 5.3 (3.3 miles) and 7.5 km (4.7 miles), respectively, from the ranger shed on Chain of Craters Road. Expect a 1.5- to 2-hour walk each way to the nearest entry at Highcastle. Stay well back from the sea cliff, regardless of whether there is an active ocean entry or not. Heed the National Park warning signs.

During the week ending March 31, three earthquakes were felt on Hawai`i Island. A magnitude-2.4 quake occurred 15 km (9 miles) northeast of Waiki`i at a depth of 15 km (9 miles) at 9:44 p.m. on Monday, March 28; it was felt at Kamuela. A magnitude-2.7 earthquake occurred 12 km east of Holualoa (Hualalai) at a depth of 29 km (18 miles) at 10:11 a.m., also on Monday; it was felt at Kalaoa. Another magnitude-2.4 quake occurred 5 km (3 miles) southeast of Kilauea summit at a depth of 25 km (15 miles) at 7:19 a.m. on Wednesday, March 30; it was felt in Volcano village.

Mauna Loa is not erupting. During the week ending March 30, seven earthquakes were recorded beneath the summit area, only one of which was deep and long-period in nature. Inflation also continues beneath the summit.

This article was written by scientists at the U.S. Geological Survey’s Hawaii Volcano Observatory and is republished by with permission.

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